Getting constant expression is required message

I have teh following string variable: tUserEmail, email id gets assigned at run time
tUserEmail = "Newuser@tyson.net"
I am trying to concatenate the tUserEmail with the other hardcoded emailID, when i do that getting the error message.

Const ToAddress As String = tUserEmail & ",jsmith@tyson.net"
getting error message; contant expression is required.
 
Thank you very much for the helpful info.
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